Intervention in bodily processes is often required to aid or control the body for one reason or another. Such intervention may be therapeutic in the sense of administering fluids for improvement in body condition. One widely employed intervention is the delivery of oxygen to a person to aid in his breathing.
In the past, it has been common to deliver oxygen to a person needing such therapy by enclosing the nose and mouth of the individual needing such treatment with a "tent." Oxygen is supplied to the interior of the tent so that the person inhales an oxygen enriched gas. A nasal cannula has been utilized to avoid the tent, but for patients confined to bed, the supply of oxygen to the cannula was also at a fixed rate. The supply of oxygen in such structures was regulated to be substantially constant.
It is usual for a patient to tell his doctor that "I feel fine sitting around and watching TV, but when I get up and start walking, I get out of breath." The physician then makes pulmonary function tests and determines that the individual needs supplemental oxygen. The outcome of these initial tests are variable, depending on the individual, and it is frequently determined that the individual needs one liter a minute of supplemental oxygen while sedentary. However, to be on the safe side, the physician will typically write a prescription for two liters a minute in order to make sure that the patient receives adequate oxygen when he is active. As used in this application, "supplemental" means in addition to that supplied naturally in the ambient air. One reason an excess of oxygen is prescribed is because there is a known limit on the rate of increase of heart rate in response to decrease in blood oxygen. This means that an increase in activity causes a decrease in blood oxygen and this causes an increase in heart rate, but that increase in heart rate is limited. Respiratory rate is substantially proportional to heart rate and thus breathing rate sensitive oxygen additions are not fully responsive to the need for blood oxygen.
It is not good therapeutic practice to prescribe more oxygen than the patient needs. It is desirable to prescribe the proper amount, and utilize a delivery system, such as disclosed herein for increasing the supply when the patient needs more oxygen. Normally, conservation is not important because the supply is large and inexpensive. However, when the patient is ambulatory and is receiving his oxygen from a small pressure bottle, or is otherwise on a limited oxygen supply, conservation is desirable. In accordance with an additional and optional structure, the system also has a breath sensor so that oxygen is only delivered upon inhalation and the number of inhalations between oxygen supply pulses is a function of sensed activity. In accordance with this invention, the therapeutic delivery system is sensitive to physical activity by the patient and increases the supply of fluid for medical intervention, which is oxygen in accordance with the preferred embodiment disclosed herein.